The disclosure relates generally to a hot/cold plate apparatus, and more particularly, to a hot/cold plate apparatus for improving the critical dimension uniformity of a substrate.
Controlling the critical dimension (CD) uniformity is becoming ever more important in integrated circuit manufacturing processes, particularly during photolithography processes as line widths of resist patterns fall within the deep sub-micron range. Various processing parameters, for example, the amount of exposure to light, developing time, and heating temperatures, affect the critical dimension uniformity.
In a lithography process, which typically includes one or more heating steps both before (pre-exposure heating) and after (post-exposure heating) the exposure step, the wafer or substrate is typically placed on or proximate to a hot plate, which includes several (often up to ten) individual heating elements for producing heat at various locations in the hot plate. The heat experienced by the photoresist layer formed over the substrate, however, is not always uniform. This non-uniform temperature distribution may be caused by various factors, for example, the distance the heat energy must travel through each media (e.g., from heating element to the top surface of the hot plate), and the condition of the hot plate surface (e.g., uniformly flat or smooth). The non-uniform temperature distribution across the photoresist layer may lead to localized variations in critical dimensions (e.g., profile shape and line and space width of the photoresist pattern), which may lead to low device yields.
Just as important as the uniform temperature distribution is for a substrate during a heating event, the temperature distribution across the substrate should be sufficiently uniform during a cooling event in order to prevent damage to the substrate such as warpage or cracking.
For these reasons and other reasons that will become apparent upon reading the following detailed description, there is a need for an improved hot/cold plate apparatus and method for uniformly heating/cooling a substrate that avoids the critical dimension uniformity issue associated with conventional hot/cold plates.